Simulated Moving Bed (SMB) technology for adsorption processing was first developed in the late 1950s for the separation of petrochemicals. Since that time, a number of SMB systems have been commercialized and the method has been applied to adsorption chromatography, ion exchange chromatography, ion exclusion chromatography, size exclusion chromatography and other chromatographic techniques. SMBs are currently used in the food, pharmaceutical, chemical, petrochemical, and other industries. The operating scheme for a binary separation is shown in FIG. 1. The boxes in the figures represent either adsorption columns, or sections of a column separated by a space with appropriate withdrawal and feed lines. The simulation of bed movement is obtained either by switching all the feed and withdrawal ports in the same direction as the fluid flow at regular switching times, tsw, or by moving the adsorbent column. This switching can be seen by comparing the system in parts a, b, c, and d. Regions between withdrawal and feed points are called zones. Each zone has a different function in the separation. Although FIG. 1 shows a simple system with one column or section per zone, it is also common to have multiple columns or sections per zone. Upon completion of the steps in FIG. 1, the cycle repeats itself over and over. Eventually a cyclic steady state is reached and the average concentrations are similar to those that would be obtained if the bed were actually moving continuously. Thus, the movement of the bed is xe2x80x9csimulated.xe2x80x9d
The four-zone system shown in FIG. 1 is an effective separation device. However, it is limited to binary separations. Thus, in FIG. 1 the feed (F) contains two solutes, A and B, that are split into an A product and a B product. If there is a third component in the feed, it will appear in one or both of the two product streams. Because ternary mixtures arise naturally, there is a desire for an effective ternary separation technique in many industries. The most obvious approach to separate ternary mixtures is to connect two 4-zone SMB systems together. The two obvious methods to do this are shown in FIG. 2. Solute A is the least strongly adsorbed, B is the middle solute, and C is the most strongly adsorbed solute. D is the desorbent, which in aqueous systems is often water. D may or may not be adsorbed. Although the switching of ports or movement of columns is not shown in FIG. 2, it is understood to occur. Multiple columns may be employed in each zone. The two trains may differ from each other and have different numbers of columns per zone, different column diameters and lengths, different adsorbents, and different switching times. The approaches shown in FIG. 2 are seldom employed in commercial practice, because the capital cost and desorbent usage for both schemes is high. Thus, there is major industrial interest in developing methods that are superior to those in FIG. 2.
SMB systems with different numbers of zones (e.g., 2, 3, 5, and 9) are also well known. A 3-zone system for binary separation is shown in FIG. 4. Two 3-zone systems could replace the 4-zone system in FIGS. 2(a) and 2(b).
An improved nine-zone system was recently developed. The scheme used a single train with nine zones and employed a recycle stream. A similar nine-zone scheme is redrawn in FIG. 3 using two trains to allow for more flexibility in operating conditions. FIG. 3 shows a method where the more strongly adsorbed components, B and C plus desorbent D, are fed to the second train. One can also build a scheme where the less adsorbed components, A and B plus desorbent D, are fed to the second train.
In one aspect, the present invention provides a system for performing a separation of a feed stream that contains at least three components. In one embodiment, the system includes a simulated moving bed separation apparatus adapted to discharge at least two streams, the at least two streams including a first discharge stream containing all the components except that it does not contain substantial amounts of a least retained component, and a second discharge stream containing all the components except that it does not contain substantial amounts of a most retained component, thus effecting a substantial separation of the least retained component from the most retained component.
In another embodiment, the system includes a first simulated moving bed separation apparatus and a second simulated moving bed separation apparatus, the first simulated moving bed separation apparatus adapted to discharge at least two streams, the at least two streams including a first discharge stream containing all the components except that it does not contain substantial amounts of a least retained component, and a second discharge stream containing all the components except that it does not contain substantial amounts of a most retained component, thus effecting a substantial separation of the least retained component from the most retained component. At least one of the first or second discharge streams becomes a feed stream for the second simulated moving bed separation apparatus. Optionally, the at least two streams from the first simulated moving bed separation apparatus include a third discharge stream that contains the least retained component and no substantial amounts of any other component and a fourth discharge stream that contains the most retained component and no substantial amounts of any other component. Preferably, the second simulated moving bed separation apparatus includes a first discharge stream containing all the components except that it does not contain substantial amounts of a least retained component, the second simulated moving bed separation apparatus further includes a second discharge stream containing all the components except that it does not contain substantial amounts of a most retained component, and wherein the second simulated moving bed separation apparatus further includes a third discharge stream taken from between the first and second feed streams of the second simulated moving bed separation apparatus. Preferably, the third discharge stream from the second simulated moving bed separation apparatus contains all the components except that it does not contain substantial amounts of either the least retained component or the most retained component. Optionally, the simulated moving bed separation apparatuses may be configured into a loop.
In another aspect, the present invention provides a process for performing a separation. In one embodiment, the process includes feeding a stream that contains at least three components into a simulated moving bed separation apparatus; substantially separating a least retained component from a most retained component; and discharging at least two streams. The at least two streams include a first discharge stream containing all the components except that it does not contain substantial amounts of the least retained component, and a second discharge stream containing all the components except that it does not contain substantial amounts of the most retained component.
In another embodiment, the process includes feeding a stream that contains at least three components into a first simulated moving bed separation apparatus; substantially separating a least retained component from a most retained component; discharging at least two streams, the at least two streams including a first discharge stream containing all the components except that it does not contain substantial amounts of the least retained component, and a second discharge stream containing all the components except that it does not contain substantial amounts of the most retained component; and delivering at least one of the first or second discharge streams as a feed stream for a second simulated moving bed separation apparatus. Optionally, the at least two streams from the first simulated moving bed separation apparatus include a third discharge stream that contains the least retained component and no substantial amounts of any other component and a fourth discharge stream that contains the most retained component and no substantial amounts of any other component. Preferably, the second simulated moving bed separation apparatus includes a first discharge stream containing all the components except that it does not contain substantial amounts of a least retained component, the second simulated moving bed separation apparatus further includes a second discharge stream containing all the components except that it does not contain substantial amounts of a most retained component, and wherein the second simulated moving bed separation apparatus further includes a third discharge stream taken from between the first and second feed streams of the second simulated moving bed separation apparatus. Preferably, the third discharge stream from the second simulated moving bed separation apparatus contains all the components except that it does not contain substantial amounts of either the least retained component or the most retained component. Optionally, the simulated moving bed separation apparatuses may be configured into a loop.
In another aspect, the present invention provides a process for feeding a simulated moving bed separation apparatus. The process includes providing a simulated moving bed separation apparatus having a switch time tsw, a normal feed flow rate rn, a desorbent flow rate, a raffinate flow rate, and an extract flow rate; feeding a stream that contains at least two components into the simulated moving bed separation apparatus for a partial feed time tpf at a partial feed flow rate rpf, wherein the partial feed time tpf is less than the switch time tsw; and maintaining at least one of the flow rates for desorbent, raffinate, or extract at the normal rate for normal feed flow conditions. Preferably, the process includes maintaining the flow rates for desorbent and extract at normal rates for normal feed flow conditions. Preferably, the partial feed flow rate rpf is about equal to or greater than the product of the switch time tsw and the normal feed flow rate rn divided by the partial feed time tpf.
In another aspect, the present invention provides a process for increasing the purity of the most retained component from a simulated moving bed separation apparatus compared to the purity of the component under normal operating conditions. The process includes providing a simulated moving bed separation apparatus having a switch time tsw and a normal feed flow rate rn; and feeding a stream that contains at least two components into the simulated moving bed separation apparatus for a partial feed time tpf at a partial feed flow rate rpf, wherein the partial feed time tpf is less than the switch time tsw, and the majority of the feed occurs in the first half of the switch time.
In another aspect, the present invention provides a process for increasing the recovery of the least retained component from a simulated moving bed separation apparatus compared to the recovery of the component under normal operating conditions. The process includes providing a simulated moving bed separation apparatus having a switch time tsw and a normal feed flow rate rn; and feeding a stream that contains at least two components into the simulated moving bed separation apparatus for a partial feed time tpf at a partial feed flow rate rpf, wherein the partial feed time tpf is less than the switch time tsw, and the majority of the feed occurs in the first half of the switch time.
In another aspect, the present invention provides a process for increasing the purity of the least retained component from a simulated moving bed separation apparatus compared to the purity of the component under normal operating conditions. The process includes providing a simulated moving bed separation apparatus having a switch time tsw and a normal feed flow rate rn; and feeding a stream that contains at least two components into the simulated moving bed separation apparatus for a partial feed time tpf at a partial feed flow rate rpf, wherein the partial feed time tpf is less than the switch time tsw, and the majority of the feed occurs in the last half of the switch time.
In another aspect, the present invention provides a process for increasing the recovery of the most retained component from a simulated moving bed separation apparatus compared to the recovery of the component under normal operating conditions. The process includes providing a simulated moving bed separation apparatus having a switch time tsw and a normal feed flow rate rn; and feeding a stream that contains at least two components into the simulated moving bed separation apparatus for a partial feed time tpf at a partial feed flow rate rpf, wherein the partial feed time tpf is less than the switch time tsw, and the majority of the feed occurs in the last half of the switch time.
In another aspect, the present invention provides a process for increasing the purity and recovery of the most and the least retained components from a simulated moving bed separation apparatus compared to the purity and recovery of the most and the least retained components under normal operating conditions. The process includes providing a simulated moving bed separation apparatus having a switch time tsw and a normal feed flow rate rn; and feeding a stream that contains at least two components into the simulated moving bed separation apparatus for a partial feed time tpf at a partial feed flow rate rpf, wherein the partial feed time tpf is less than the switch time tsw, and the majority of the feed occurs in the middle two quarters of the switch time.
This feed process is applicable to all types of SMB systems including binary separations, multi-component separations, and any number of zones. This process can also be used for the feed to the second train, the third train, or any train of a cascade system (e.g., FIGS. 7-12). For this case, the discharges can be collected in separate tanks, then the new feed process can be used. The feed process may be particularly useful, for example, in high pressure liquid chromatography (HPLC) and supercritical fluid separations.
In another aspect, the present invention provides a process for performing a separation. The process includes providing a simulated moving bed separation apparatus having a switch time tsw and a normal feed flow rate rn; feeding a stream that contains at least two components into the simulated moving bed separation apparatus for a partial feed time tpf at a partial feed flow rate rpf, wherein the partial feed time tpf is less than the switch time tsw; substantially separating a least retained component from a most retained component; and discharging at least two streams, the at least two streams including a first discharge stream containing all the components except that it does not contain substantial amounts of the least retained component, and a second discharge stream containing all the components except that it does not contain substantial amounts of the most retained component. Preferably, the partial feed flow rate rpf is about equal to the product of the switch time tsw and the normal feed flow rate rn divided by the partial feed time tpf.
Definitions
As used herein, xe2x80x9cSMBxe2x80x9d means xe2x80x9csimulated moving bed.xe2x80x9d
As used herein, xe2x80x9cswitch time (tsw)xe2x80x9d means the total time between activation of switching valves to change flow between columns.
As used herein, xe2x80x9cnormal feed flow rate (rn)xe2x80x9d means the volumetric rate of flow of feed being introduced into the SMB when feed is introduced into the SMB during the entire switch cycle under standard operating conditions.
As used herein, xe2x80x9cpartial feed time (tpf)xe2x80x9d means the length of time that feed is introduced during each switching cycle.
As used herein, xe2x80x9cpartial feed flow rate (rpf)xe2x80x9d means the volumetric rate of flow of feed being introduced into the SMB during the partial feeding time.
As used herein, xe2x80x9craffinatexe2x80x9d is a product stream pumped from the SMB during operation that corresponds to the least retained component.
As used herein, xe2x80x9cextractxe2x80x9d is a product stream pumped from the SMB during operation that corresponds to the most retained component.
As used herein, xe2x80x9cdesorbentxe2x80x9d is an eluent or mobile phase used to carry out the separation by moving the solute through a column.
As used herein, xe2x80x9cpartial feed systemxe2x80x9d means an SMB system that has a partial feed time tpf at a partial feed flow rate rpf, wherein the partial feed time tpf is less than the switch time tsw. Preferably, the partial feed flow rate rpf is about equal to or greater than the product of the switch time tsw and the normal feed flow rate rn divided by the partial feed time tpf.
The present invention provides for separation of components from a stream containing at least three components (e.g., A, B, . . . , and Z) resulting in at least two streams, one stream containing all the components except that it does not contain substantial amounts of the least retained component (A), and another stream containing all the components except that it does not contain substantial amounts of the most retained component (Z), thus effecting a separation of the least retained component (A) from the most retained component (Z). For example, an easy split of a stream containing a ternary mixture of A, B, and C results in one stream containing A and B, and another stream containing B and C. Similarly, an easy split of a stream containing a quaternary mixture of A, B, C, and Z results in one stream containing A, B, and C, and another stream containing B, C, and Z.
As used herein, the expressions xe2x80x9ccontaining all the componentsxe2x80x9d and xe2x80x9ccomprising all the componentsxe2x80x9d are used interchangeably, and refer to the compositions of the indicated streams. The terms are not meant to imply that the entire amount of any component is present in the indicated stream.
As used herein, xe2x80x9csubstantial separation of two componentsxe2x80x9d means that each component contains no more than about 20% by weight of the other component, preferably no more than about 5% by weight of the other component, and more preferably no more than about 1% by weight of the other component
As used herein, xe2x80x9ca stream that does not contain substantial amounts of a componentxe2x80x9d means that the stream contains at most about 20% by weight of the component, preferably at most about 5% by weight of the component, and more preferably at most about 1% by weight of the component.